The lymphatic system is part of the circulatory system in conjunction with the arterial and venous systems. A primary function of the lymphatic system is to drain excessive interstitial fluid back into the venous system at two main locations: the thoracic duct and the lymphatic duct, which drain into the left and right subclavian veins, respectively.
Under normal circulatory conditions of the arterial and venous systems the interstitial fluid volume balance is maintained and the lymph fluid is cleared back through the lymphatic system. In pathological conditions such as Acute Cardiogenic Pulmonary Edema and chronic heart failure, the capillary hydrostatic pressure and the venous pulmonary pressure can become elevated and fluid flows excessively out of the blood vessels and into the interstitial and alveolar spaces. The pressure gradient between the initial lymphatics and at the outflow of the thoracic duct and the lymphatic duct is reduced and the lymphatic system cannot clear the additional fluid which accumulates in the air spaces of the lungs. This is a life threatening condition as gas exchange is impaired to the extent that it may lead to respiratory failure.
Current treatment methods require extended hospitalization and treatment with loop diuretics and/or vasodilators. Oftentimes patients must also receive supplemental oxygen or, in more extreme cases, require mechanical ventilation. Many of these treatment methods are less than ideal because the edema is not always alleviated rapidly enough and for many patients renal function is adversely affected. A significant percentage of patients do not respond to this treatment and a significant percentage must be readmitted to a hospital within thirty days.
A significant problem with current treatment protocol is that it is based on the need to reduce intravascular blood pressure to move interstitial and lymphatic fluid back into the vasculature. The reduction of intravascular blood pressure may lead to hypotension and may activate the Renin Angiotenesin Aldesterone System, which may lead back to an increase in blood pressure or to worsening of renal function. Eventually, this cycle leads to diuretic resistance and the worsening of renal function in almost 30% of admitted patients. The lymphatic system can directly drain fluids from the interstitial compartment into the intravascular compartment and by such to relief edema.
The lymphatic system drains the interstitial fluids via the thoracic duct and right lymphatic duct that drain into the region around the bifurcation of the left subclavian vein and left internal jugular vein for the thoracic duct and into the bifurcation of the right internal jugular vein and right subclavian vein for the right lymphatic duct. However, in conditions such as acutely decompensated heart failure the lymphatic return is reduced as a result of elevated central venous pressure (CVP). Therefore, as a result of the elevated CVP, the lymphatic return is greatly reduced.
Accordingly, there remains a need for improved systems and methods for reducing pressure at an outflow of a duct such as the thoracic duct or the lymphatic duct.